The term “Guerbet alcohols” is commonly used to describe alcohols formed by Guerbet reaction, named after Marcel Guerbet, which is an auto condensation converting a primary aliphatic alcohol into its β-alkylated dimer alcohol with loss of one equivalent of water. The Guerbet reaction requires a catalyst and elevated temperatures.
Guerbet alcohols are saturated primary alcohols with a defined branching of the carbon chain. They are well known in the state of the art.
The term Guerbet alcohol as used in this specification is to be understood as a monofunctional, primary alcohol comprising at least one branching at the carbon atom adjacent to the carbon atom carrying the hydroxyl group. Chemically, Guerbet alcohols are described as 2-alkyl-1-alkanols, but in the present specification Guerbet alcohols comprise also multi-branched alcohols (multiple alkyl alcohols).
The reaction mechanism leading to Guerbet alcohols comprises essentially the following steps: First, a primary alcohol of the formula RCH2CH2OH, wherein R may be hydrogen or a straight or branched chain alkyl group, is dehydrogenated (or oxidised) to the respective aldehyde. In the following, two aldehyde molecules undergo an aldol condensation to an α,β-unsaturated aldehyde, which is finally hydrogenated to the “dimer” alcohol. The catalyst used for this reaction may be of alkaline nature (e.g. potassium hydroxide, sodium hydroxide, sodium tert-butoxide, etc.) possibly in the presence of a platinum or palladium catalyst. Usually the reaction takes place under heating and possibly pressurization. An overview of a Guerbet condensation process is given in the illustration below:

A Guerbet alcohol may also have two or more branches, particularly if it is the product of two or more subsequent condensation reactions. For example, 2-ethyl-1-hexanol, the Guerbet dimer of 1-butanol, may react with 1-propanol to yield 4-ethyl-2-methyl-1-octanol. This further increases the variety of Guerbet alcohols.
An example of a process for preparing branched dimer alcohols based on the Guerbet reaction is for instance disclosed in the patent specification EP 0 299 720 B1 assigned to Exxon Chemical Patents Inc. The process comprises steps of first combining the primary alcohol mixture with KOH and NaOH and heating the mixture until the base dissolves. Thereafter a platinum catalyst on activated carbon support is added and heated to reflux with water being evolved and removed as it is formed.
Another example of a process for dimerizing alcohols in a manner of Guerbet reaction is disclosed in patent application US 2012/0220806 A1 filed by Cognis IP management GmbH. The process converts one or more starting alcohols having 2 to 72 carbon atoms and one to three OH-groups per molecule in the presence of a base (KOH), a carbonyl compound and a metallic hydrogenation catalyst. The process is limited to the use of alcohols that have at least one primary or secondary OH-group and a carbon atom bearing at least one hydrogen atom as a substituent that is directly adjacent to the carbon atom having the primary or secondary OH-group.
For a large scale production of multi-branched Guerbet alcohols, however, an improved manufacturing process is required that further allows to control the final distribution of Guerbet alcohols with respect to carbon number and branching type and number.